This heading explicitly excludes heating resistors — elements whose primary purpose is to generate heat (such as those used in electric heaters or ovens). Those classify in the chapter on electrothermal appliances. Resistors here are circuit-control components designed to limit or regulate current, not to produce heat as an end use.

The 20 W power handling capacity is the tariff schedule's dividing line between subheadings for both fixed NESOI resistors (853321 vs. 853329) and wirewound variable resistors (853331 vs. 853339). Importers should confirm the rated maximum continuous power dissipation from the manufacturer's datasheet, as this figure — not peak or surge ratings — determines the correct subheading.